Circuit Description
When the ignition is turned ON, the key is tested by the immobilizer anti-theft system. While the key code is being read by the immobilizer control unit, the engine can start and run with any key that will turn the lock cylinder. The key code is read and compared with key codes that have been stored in the memory of the immobilizer control unit. If a valid key is detected, the immobilizer control unit sends a serial data release message to the electronic control module (ECM). Included in the release message is an identification (ID) code which assures that neither the immobilizer control unit nor the ECM has been substituted to defeat the system. If the ECM receives an invalid release message, the ECM disables the fuel injector circuit.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1628 -- Theft Deterrent Start Enable Signal Not Received
Conditions for Setting the DTC
| • | The ECM does not receive the signal from the immobilizer control module within 1.260 seconds after the ignition is turned on. |
| • | The above conditions are maintained until the ignition is switched OFF. |
Conditions for Clearing the MIL/DTC
The ignition switch is turned OFF or the scan tool TROUBLE CODE CLEAR command is issued.
Step | Action | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Theft Deterrent System Schematics | |||||||||
1 | Did you perform the Diagnostic System Check-Vehicle? | Go to Step 2 | |||||||
2 |
Is communication established between the scan tool and the immobilizer control unit? | Go to Step 3 | Go to Scan Tool Does Not Communicate with High Speed GMLAN Device | ||||||
3 | Read the IMMO & ECM ID CODE message that was displayed after requesting DIAGNOSIS. Did the message differ from normal message? Normal Message:
| Go to Scan Tool Does Not Communicate with High Speed GMLAN Device | Go to Step 4 | ||||||
4 | Check for an open serial data wire between the immobilizer control unit and the ECM. Was the circuit open? | Go to Step 5 | Go to Step 6 | ||||||
5 | Repair the open serial data wire between the ECM and the immobilizer control unit. Is the repair complete? | Go to Step 8 | |||||||
6 | Replace the immobilizer. 2. Reprogram the identification (ID) code. Refer to "Identification (ID) Code Reprogramming" in this section. Is the repair complete? | Go to Step 8 | Go to Step 7 | ||||||
7 | Replace the ECM. 2. Turn the ignition ON, OFF for more than 4 seconds. 3. Turn the ignition ON. Is the repair complete? | Go to Step 8 | |||||||
8 | Operate the vehicle to verify the repair is complete. Do any DTC's set? | System OK | |||||||
